1. Field of the Invention
This invention relates to a coil type contactor, as well as a connector using the same, which is suitable to be used for achieving an electrical connection with a leadless type IC package such as an LGA IC package, a BGA IC package or the like.
2. Prior Art
Mounting methods for electric parts have progressed so as to include planar mounting methods. The configuration of the electric part in the planar mounting methods in thus suitable for the planar mounting. In an LGA IC package and a BGA IC package, wiring patterns and soldering balls are densely arranged on a rear surface of the package. In the case of the LGA package, since wiring patterns are made in a state in which no convexities and no concavities are present on a flat rear surface of the package, it is technically difficult to connect the rear surface of the package to a wiring board by closely contacting the former directly to the latter. Therefore, a connector is definitely necessary for connecting the package to the wiring board. Also in the case of the BGA package, it is customary that the package is connected to the connecting pattern surface of the wiring board by means of soldering balls, or with the use of a connector.
In general, the basic construction of a connector used, for those IC packages is such that a contact point formed on a rear surface of the IC package is vertically pressed for connection with a contact portion of the wiring board via a contactor embedded in a connector. A restoring resilient force generated as a reaction when the contactor embedded in the connector is compressed serves as a contacting force. Therefore, the connector is normally sandwiched for use between the IC package and the wiring board, and is of a plate-like configuration capable of covering the entire surface of the contact portion. As one of the contactors which are vertically compressed, there can be contemplated a coil-like contactor formed of a coil spring.
Furthermore, due to the progression toward miniaturization and high function of ICs, contactors are required to be embedded in a connector at a high density. For example, a distance between adjacent contactors which are arranged in a vertical and horizontal pattern is required to be 1 mm and even 0.5mm in some cases. The number of the contactors to be arranged is usually 100 to 200. In some cases, the number of the contactors exceeds 300.
For surface mounting an IC package with a connector sandwiched between a wiring board and the IC package, an upper limit of a compressive force of a whole connector is required to be reduced in view of mechanical strength of the IC package when the IC package is miniaturized. For example, if a contacting force (compressive force) of a single contactor in a connector is 50 g, a contacting force of 15 kg is needed for 300 contactors. This is practically impossible to employ in view of the design of an apparatus. In the case of a multi-core connector having more than 200 pins, it becomes necessary to reduce the contacting force to 30 g in order to reduce the total compressive force. A contacting force of 30 g is a minimum contacting force for maintaining a stable contacted-state, and the spring characteristics of the contactor is important to contact reliability. A contactor satisfying such requirement is low in spring constant and high in flexibility. It is important that the contacting force is not greatly changed even when the compressive dimension is changed due to the dimensional change of an IC. With reference to an embodiment, it is preferable that the length of the contactor is from 1.5 mm to 2.0 mm when the contactor is in a compressed-state, and a compressive force of from 30 g to 40 g is generated when the contactor is compressed to between 70% and 60%.
This invention aims at the development of a contactor, as well as a connector using the same, which satisfies the above- mentioned conditions and which uses a spring capable of a vertical displacement, such as a coil spring to be described hereinafter.
In general, the coil spring can be a spring which is vertically flexed in the actual designing of the spring, i.e., as a "spring element" which is greatly deformed only in a Z-direction, which takes little space in X- and Y-directions, and which is not changed in dimension in the X- and Y-directions upon compression. However, since a coil spring is very long in electrically-conductive path length and overly large in inductance (L component), it cannot be used as a contactor. It came to the mind of the present inventor that if a coil spring having only a negligible amount of L component is made by improving this coil spring, a contactor having a high flexibility and a low spring constant may be developed. The present invention has been accomplished based on this finding.